Aquaporins are cell membrane proteins that act as molecular water channels to mediate the flow of water in and out of the cells. While there is some degree of passive diffusion or osmosis of water across cell membranes, the rapid and selective transport of water in and out of cells involves aquaporins. These water channels selectively conduct water molecules in and out of the cell, while blocking the passage of ions and other solutes, thereby preserving the membrane potential of the cell. Aquaporins are found in virtually all life forms, from bacteria to plants to animals. In humans, they are found in cells throughout the body.
Aquaporin inhibitors, e.g., inhibitors of AQP4 and/or AQP2, may be of utility in the treatment or control of diseases of water imbalance, for example edema (particularly edema of the brain and spinal cord), hyponatremia, and excess fluid retention, as well as diseases such as epilepsy, retinal ischemia and other diseases of the eye, myocardial ischemia, myocardial ischemia/reperfusion injury, myocardial infarction, myocardial hypoxia, congestive heart failure, sepsis, and neuromyelitis optica, as well as migraines.
Prior to Applicants' filings, there have been no known specific, validated inhibitors of aquaporins, for example AQP4 or AQP2. Certain antiepileptic or sulfonamide drugs (e.g., acetylsulfanilamide, acetazolamide, 6-ethoxy-benzothiazole-2-sulfonamide, topiramate, zonisamide, phenytoin, lamotrigine, and sumatriptan) were at one point reported to be possible inhibitors of AQP4, but this later proved to be incorrect. Yang, et al., Bioorganic & Medicinal Chemistry (2008) 16: 7489-7493. No direct inhibitors of AQP2 have been reported.
Thus, there is a need for compounds that selectively inhibit aquaporins. In addition, there is a need for compounds that may be formulated to deliver compounds that selectively inhibit aquaporins, for example compounds which may be soluble in aqueous media and/or may be administered easily to patients.